1. Field of the Invention
The present invention relates to a balun that performs conversion between unbalanced and balanced signals, and in particular relates to a thin film balun that is formed by a thin film process advantageous for smaller and thinner models.
2. Description of the Related Art
A wireless communication device includes various high frequency elements such as an antenna, a filter, an RF switch, a power amplifier, an RF-IC, and a balun. Of these elements, a resonant element such as an antenna or a filter handles an unbalanced signal which is based on a ground potential, whereas an RF-IC which generates or processes a high frequency signal handles a balanced signal. Accordingly, when connecting these two elements, a balun that functions as an unbalanced-balanced converter is used.
There is a tendency to require that a balun used for a wireless LAN or a mobile communication device such as a mobile phone has filter characteristics (attenuation characteristics) of attenuating desired frequencies. To impart such attenuation characteristics, a technique of providing a capacitor between a balanced terminal and a GND terminal or between an unbalanced terminal and a GND terminal of the balun is disclosed (for example, see Japanese Patent Application Laid-Open No. 2004-274715).